1. Field of the Invention
The present invention relates to a semiconductor device using a new and improved wiring material and, more particularly, to a wiring material of a semiconductor device and a method for forming a wiring pattern therewith, wherein a self diffusion phenomenon and a creep phenomenon which are caused by stress between a wiring material and a passivation film can be reduced.
2. Description of the Prior Art
Conventionally, aluminum or an alloy of aluminum and silicon is used as a wiring material of a semiconductor device. A passivation film is formed on an Al alloy wiring layer (including an Al wiring layer) to protect a semiconductor element. A silicon nitride (SiN) film formed by plasma CVD is receiving a great deal of attention as a passivation film formed on a wiring layer since the SiN film prevents external contamination and can be formed at a low temperature. Furthermore, such a SiN film has high reliability, good workability and good step coverage.
However, when a silicon nitride film is formed by plasma CVD on a wiring layer, an Al alloy tends to disappear. This phenomenon occurs when annealing is performed on a structure (FIG. 1) wherein a lower wiring layer 2 is formed on a substrate 1 having a semiconductor device thereon, an upper wiring layer 3 is formed on the lower wiring layer 2 through an insulating layer 6 so as to cross the lower wiring layer 2, and a silicon nitride film 4 is formed on the upper wiring layer 3 by plasma CVD. As is apparent from FIG. 2, narrowed portions 5 are formed in the upper wiring layer 3 at intersections between the upper and lower wiring layers 3 and 2 as if the wiring material has disappeared. The number of narrowed portions increases upon annealing at a temperature of 500.degree. C. for about 10 minutes. Therefore, annealing conditions in the manufacture of semiconductor devices are greatly restricted.
This phenomenon occurs due to thermal stress which is caused by a difference between thermal expansion coefficients of the silicon nitride film and the wiring layer. The stress can be decreased by increasing the content of silicon in the silicon nitride film. In this case, however, the electrical characteristics of the silicon nitride film as the passivation film are degraded, resulting in a disadvantage.